1. Field of the Invention
This invention relates to an information processing apparatus, method, and a program, and more particularly to an information processing apparatus, method, and a program by which data can be communicated.
2. Description of the Related Art
General communication through a LAN (Local Area Network) or the like assumes that particular data packets do not occupy a transmission line and data packets corresponding to a plurality of services can be transmitted at any time. Therefore, it should be taken into consideration for each service by what degree the packet loss or packet delay arising from collision between data packets during transmission of data packets can be permitted. Accordingly, although the packet loss or packet delay does not make a serious problem to transmission of data packets corresponding to services for which the real time performance is not necessary, it makes a serious problem to transmission of data packets corresponding to services for which the real time performance is necessary.
The real time performance signifies to satisfy a restrictive condition that a predetermined process is completed within a fixed period of time, that is, a temporal restriction.
Several methods have been proposed to solve the problem described above. One of such methods is disclosed, for example, in Japanese Patent No. 3385899 entitled “Real Time Communication Method” (hereinafter referred to as Patent Document 1). Another method is disclosed, for example, in Japanese Patent No. 1963910 entitled “Multimedia LAN System” (hereinafter referred to as Patent Document 2). According to the “Real Time Communication Method” of Patent Document 1, a data packet for which the real time performance is necessary is transmitted within a predetermined period of time which appears periodically. The real time performance is assured by calculating and setting the amount of data which can be transmitted within the predetermined period of time so that the data amount may be equal to or lower than a predetermined value. Meanwhile, according to the “Multimedia LAN System” of Patent Document 2, a synchronous control time slot, a synchronous transfer time slot, and an asynchronous transfer time slot common to an entire LAN system are provided, and the real time performance of data packets which are transmitted using the synchronous transfer time slot is assured.
On the other hand, in recent years, where a process is executed between and by different apparatus connected to a network, the real time performance is sometimes necessary not only for a process by the sender side but including a process by the receiver side. For example, an operation as to change over a plurality of image changeover apparatus so as to change over image signal outputs of them at a time in a particular image frame is controlled from a control apparatus through a network. In such a case, it is necessary not only for the control apparatus of the sender side to transmit a pertaining control data packet within a fixed period of time but also for the image changeover apparatus on the receiver side to receive the control data packet and execute a process based on the control data packet within the same fixed period of time.
It is to be noted that, in the following description, that the real time performance is necessary including processes not only by the sender side but also by the receiver side in this manner is hereinafter referred to also as demand for transmission and reception assurance within a predetermined period of time.